Multiple actuator pivot bearing

ABSTRACT

A split shaft assembly for vibration control between multiple actuator pivots in a disk storage device. A first actuator pivot is mounted on a first shaft unit and a second actuator pivot is mounted on a second shaft unit. The second shaft unit is mated to the first shaft unit in axial alignment along a common pivot axis by a separating portion of a vibration control material, which interrupts transmission of vibrational force between the first actuator pivot and the second actuator pivot.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the manufacture of disk storagedevices. More particularly, the invention is directed to an apparatusand method for vibration control between multiple actuators as arecommonly used in such storage devices.

2. Description of the Background Art

Disk storage devices are well known in the industry today. Many versionsexist, with the most widely used probably being magnetic disk storagedevices termed “hard drives” or “fixed disk drives.” In these, one ormore disks coated with a magnetic storage media are rotated and data iswritten to and read from the media with read/write heads pivotallymounted on actuator assemblies. Optical and other types of disk storagedevices are also known or possible, and it should clearly be appreciatedthat the present invention may improve many embodiments of these aswell, but for exemplary purposes the present discussion will primarilybe directed to magnetic disk storage devices.

Modern disk storage devices often have a number of competing designgoals. Without limitation, these may include reliability, accuracy,small size, high storage density, and high data access and transferspeeds. A key portion of a disk storage device may thus be the pivot oractuator assembly or assemblies which position read/write heads over thestorage media. Traditionally, single pivot assemblies have primarilybeen used, but multiple pivot assembly systems are also known, and inseeking to reach various of the competing design goals the industry isnow turning to multiple pivot assembly systems, particularly dual pivotassembly systems.

Unfortunately, aside from the obvious additional mechanical complexity,multiple pivotal actuator assemblies introduce a number of additionalproblems for the designers of disk storage devices. Of present interestare how they create, transfer, and are effected by vibration. Beforeturning to a discussion of this, however, a brief summary of the stateof the prior art may by useful.

Vibration is a problem even in single pivot assembly systems. U.S. Pat.No. 5,930,071 by Black teaches a rubber-like material to dampenvibrations at the bearings and the shaft at which the single actuatorassembly pivots. Japanese Pat. No. 2-139772 by Hidehiro teaches a singlepivot assembly wherein the shaft has an elastic core into which a screwextends to hold the shaft in place. And Japanese Pat. No. 1-048271 byHiroshi teaches a vibo-elastic material on an outer circumference toreduce vibration from the device housing effecting a single carriage.

In notable contrast, when the industry has turned to dual pivot assemblysystems it has essentially ignored the problem vibration control, orworked around it using basic design methodologies not germane to thisdiscussion. U.S. Pat. No. 4,544,972 by Kogure et al. and Japanese Pat.No. 62-78783 also by Kogure teach dual actuator assemblies withoutvibration dampening or isolation. U.S. Pat. No. 5,761,007 by Price etal. also teaches multiple actuators, and it even uses a elastometricsleeve. But this sleeve is merely part of a crash stop against which anactuator stops its pivotal motion in one direction, rather than anymanner of vibration control. Thus multiple pivot assembly systems withvibrations control remain something unknown in the art.

As described, traditional multiple actuator designs have a dual pivotwith a single shaft. Unfortunately, the conventional single shaft usedprovides a transmission path for vibration to travel between therespective actuators. Since the use of multiple actuators is generally astraight forward extension of the principles for dual actuators, thedual actuator case will primarily be discussed herein.

FIG. 1 (background art) is a side broken view of bearing assemblies fordual actuators mounted on a single shaft, as might be found in the priorart. A common shaft 1 is provided which is mounted within a disk storagedevice housing (not shown). Respective bearing assemblies 2, one peractuator, are mounted on the common shaft 1, typically spaced apart by aseparation maintainer 3 (e.g., a spacer or bushing) as shown in FIG. 1.

The bearing assemblies 2 each include two bearings 4 which are mountedin a sleeve 5 of the actuator (also not otherwise shown). Specifically,in the embodiment shown in FIG. 1, the bearings 4 include inner races 6and outer races 7. The bearings 4 depicted in FIG. 1 are ball-typebearings, but roller-types and, at least in theory, other types ofbearings may also be employed.

As can be seen in FIG. 1, the outer races 7 of the bearings 4 arefixedly mounted in the sleeves 5 of the respective actuators, and theinner races 6 of the bearings 4 are fixedly mounted on the common shaft1. FIG. 1 also depicts one common arrangement, wherein the inner race 6of the lower-most bearing 4 in the bottom bearing assembly 2 abutsagainst a base flange 8 of the common shaft 1. The separation maintainer3 then abuts against the top-most inner race 6 of the bottom bearingassembly 2 as well as against the lower-most inner race 6 of the upperbearing assembly 2. In this manner, when the media disk in a diskstorage device is oriented to revolve in a horizontal plane, theactuators are horizontally pivotally mounted and vertically fixedlymounted on the common shaft 1.

Unfortunately, this arrangement provides a transmission path forvibration between the respective actuators. In FIG. 1, path arrows 9stylistically depict the paths for vibrational force from the upperactuator into the lower actuator. When vibration occurs in the upperactuator, for instance, it may travel through the upper sleeve 5 and thebearings 4 into the common shaft 1 and the separation maintainer 3 (inembodiments where one is used), and from these into the lower bearings 4and sleeve 5 of the lower actuator. In this manner, vibration occurringin one actuator has a continuous transmission path to any otheractuators mounted on the common shaft 1.

In practice, since both the upper and lower actuators move separately,vibration can be generated in both and interact complexly to effectactuator-mounted device operation, such as that of data read/writeheads. It should also be appreciated that vibration inherently has timeand frequency related components. Vibrational energy present at a firstinstant in time may be stored, somewhat, and have an effect at a latersecond instant in time. Vibrational energy may also be generated,transferred, and absorbed differently depending upon its frequency andits relationship to the resonant and harmonic frequencies of thephysical structures which are present.

This can cause particularly undesirable results. For example, a commonuse of multiple actuators is to separate track following and seekingfunctions in a magnetic disk storage device such as a computer harddrive. Vibrations occurring in the seeking actuator can travel to thetracking actuator and can cause heads mounted on it to go off course.Alternately, vibrations from the tracking actuator can cause an increasein the settle time for the seeking actuator. Or vibrations created in anactuator at one instant can travel outward, elsewhere into the entirestorage assembly, and be reflected back at a later time to adverselyeffect the operation of the same actuator.

The preceding is not an exhaustive list of all possible vibro-mechanicalinteractions, but it is enough to demonstrate that disk storage devicesare quite complex structures and that designers of them do not have aneasy task. If disk storage device design is to continue to evolve, usingincreasing numbers of mechanical subassemblies operating separately andin concert at increasing speeds, systems are sorely needed for vibrationcontrol. Accordingly, an object of the present invention is to provideapparatus and method for vibration control between multiple actuators indisk storage devices. Other objects and advantages will become apparentfrom the following disclosure.

SUMMARY OF THE INVENTION

The present invention relates to split shaft assemblies for vibrationcontrol between multiple actuator pivots in a disk storage device. Afirst actuator pivot is mounted on a first shaft unit and a secondactuator pivot is mounted on a second shaft unit. The second shaft unitis mated to the first shaft unit in axial alignment along a common pivotaxis by a separating portion of a vibration control material, whichinterrupts transmission of vibrational force between the first actuatorpivot and the second actuator pivot.

A more through disclosure of the present invention is presented in thedetailed description which follows and the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects and, advantages and features of the present invention willbe more clearly understood by reference to the following detaileddisclosure and the accompanying drawings in which:

FIG. 1 (background art) is a side broken view of dual actuator bearingassemblies mounted on a conventional single common shaft;

FIG. 2 is a side broken view of dual actuator bearing assemblies mountedon a split shaft mated together with a boss and flange, in accordancewith one embodiment of the present invention;

FIG. 3 is a side broken view of dual actuator bearing assemblies mountedon a split shaft mated together with an internal post, in accordancewith another embodiment of the present invention;

FIG. 4 is a side broken view of dual actuator bearing assemblies mountedon a split shaft mated together with a spacer ring, in accordance withyet another embodiment of the present invention;

FIG. 5 is a side broken view of dual actuator bearing assemblies mountedon a split shaft mated together with concentric bushings, in accordancewith yet another embodiment of the present invention;

FIG. 6 is a side broken view of dual actuator bearing assemblies mountedon a split shaft mated together with adhesively connected flanges, inaccordance with yet another embodiment of the present invention;

FIG. 7 is a side broken view of dual actuator bearing assemblies mountedon a split outer shaft units mounted on a common inner shaft, inaccordance with yet another embodiment of the present invention;

FIGS. 8a-c (prior art) are performance graphs of respective armresponses for a standard common shaft pivot assembly; and

FIGS. 9a-c are performance graphs of respective arm responses for apivot assembly according to the embodiment of the present inventiondepicted in FIG. 6.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to split shaft assemblies for vibrationcontrol between multiple actuator pivots, as may be commonly used in adisk storage device.

A preferred embodiment of the present invention is a split shaftassembly employing a vibration control material. As illustrated in thevarious drawings herein, and particularly the views of FIGS. 2-7, someexemplary embodiments of the present invention are collectively depictedby the general reference character 10.

Turning now to FIG. 2, a side broken view is shown of one pivot assembly10 according to the present invention. A split shaft assembly 12includes a bottom shaft unit 14 and a top shaft unit 16. The bottomshaft unit 14 includes a boss 18 and the top shaft unit 16 includes aflange 20. The bottom shaft unit 14 and the top shaft unit 16 are matedtogether in male-to-female manner by insertion of the boss 18 into theflange 20, but with a layer of vibration control material 22 preventingactual physical contact between any potions of the boss 18 and theflange 20 or directly between the bottom shaft unit 14 and the top shaftunit 16. The extent to which the boss 18 is inserted into the flange 20,i.e., into a hollowed out interior of the top shaft unit 16, providesdesirable stiffness to the split shaft assembly 12 as a whole in theaxial and bending directions.

In particular, the bottom shaft unit 14, the top shaft unit 16, and theentire split shaft assembly 12 share a common pivot axis 24 about whichessentially conventional actuator assemblies (or “pivot assemblies”) maybe provided. As shown in FIG. 2, a bottom actuator assembly 26 may bemounted on the bottom shaft unit 14 and a top actuator assembly 28 maybe mounted on the top shaft unit 16. These actuator assemblies 26, 28each include bearings 30 having inner races 32 and outer races 34. Thebearings 30 are further mounted into sleeves 36 of the respectiveactuator assemblies 26, 28.

In the particular variation shown in FIG. 2, the bottom shaft unit 14includes a base flange 38 against which the inner race 32 of the bottombearing 30 in the bottom actuator assembly 26 abuts. As noted, the topshaft unit 16 includes the flange 20, and the inner race 32 of the lowerbearing 30 in the top actuator assembly 28 abuts against this. In thismanner, this embodiment may dispense with the separation maintainer 3 ofFIG. 1 (background art). This is often highly desirable because spacebetween the bottom actuator assembly 26 and the top actuator assembly 28can be very constrained. The spacing shown in FIG. 2 is somewhatexaggerated compared to what will be the case in many embodiments, withthe flange 20 shown for illustrative purposes as being much thicker thanit typically needs to be.

The vibration control material 22 plays a particularly important role inall embodiments of the pivot assembly 10. It may be selected for itsability to isolate the bottom shaft unit 14 and the top shaft unit 16from vibrations, or it may be selected for its ability to dampen passingvibrations, or it may selected to provide varying degrees of isolationand dampening concurrently.

Without limitation, some representative examples of materials for use asthe vibration control material 22 are urethanes, particularly moldableones, and acrylics. The urethanes, and other synthetic “rubbers,” can beparticularly stiff and have useful isolating characteristics, whileacrylics can have useful dampening characteristics.

One interesting material is epoxy. Not all epoxies are stiff or hardento brittleness, particularly at the typical operating temperatures indisk storage devices (e.g., 65 degrees centigrade). Thus, essentiallyall polymers have some potential for use as the vibration controlmaterial 22.

The vibration control material 22 in FIG. 2 has been described above asa “layer” and is shown filling the entire region between the boss 18 andthe flange 20 portions of the bottom shaft unit 14 and the top shaftunit 16. This will likely be the case in most embodiments, but it shouldbe appreciated that these are not requirements. The vibration controlmaterial 22 separates the bottom shaft unit 14 and the top shaft unit16, but its shape and the quantity used can vary.

Turning now to FIG. 3, a side broken view of a different pivot assembly10 is depicted there. A split shaft assembly 52 is provided whichincludes a bottom shaft unit 54, a top shaft unit 56, and a post 58.Both the bottom shaft unit 54 and the top shaft unit 56 have recesses 60suitable for receiving one of respective ends 62 of the post 58. Thepost 58 is prevented from actual physical contact with the shaft units54, 56 by a layer of vibration control material 64 (which may beessentially the same as that described for the embodiment in FIG. 2).

In FIG. 3 the shaft units 54, 56 are both depicted as being hollow. Thisis not a requirement but may be motivated by the same reasons thatconventional single, common shafts are usually hollow, to save materialand to reduce weight. Being hollow here, however, also convientlyprovides the recesses 60.

While using the post 58 alone may serve to provide the split shaftassembly 52 with adequate stiffness, FIG. 3 also shows how optionalbushings may increase these characteristics and provide other benefits.

A lower bushing 66 may be provided at the upper end of the bottom shaftunit 54 and an upper bushing 68 may be provided at the lower end of thetop shaft unit 56. These may be press fit on or they may be loose, andthe upper bushing 68 may even be made an integral part of the top shaftunit 56. These bushings 66, 68 may also abut against inner races 70 ofbearings 72 in sleeves 74 of a bottom actuator assembly 76 and a topactuator assembly 78, although this is not a requirement when bushingsare used. However, as shown, vibration control material 64 is providedto separate such bushings 66, 68 when they are present. This vibrationcontrol material 64 may be the same as that used at the post 58 or itmay be different. This is a matter of design choice. But, for example,it may be a useful way to control two particular different sets ofvibration frequencies concurrently.

Much as was the case for FIG. 2, the vibration control material 64 canbe a layer and fill entire regions or it may be shaped differently andused more sparingly. The thickness of the bushings 66, 68 shown in FIG.3 is also somewhat exaggerated for illustrative purposes compared tothat which is likely to be necessary.

In summary, the versions of this embodiment, with or without the use ofthe bushings 66, 68, provides adequate stiffness in the axial andbending directions and facilitates maintaining a common pivot axis 80.

Turning now to FIG. 4, it is a side broken view of yet a different pivotassembly 10. A split shaft assembly 102 is provided which includes abottom shaft unit 104, a top shaft unit 106, and a spacer 108 which ismade of a vibration control material.

The bottom shaft unit 104 has an upper end 110 which extends past aninner race 112 of an upper bearing 114 in a sleeve 116 of a bottomactuator assembly 118. The top shaft unit 106 has a lower end 120 whichextends past the inner race 112 of a lower bearing 114 in the sleeve 116of a top actuator assembly 122.

The spacer 108 has a coaxial top opening 124 and bottom opening 126.These may be part of one common bore, as shown, or they simply mayseparate recesses. The upper end 110 of the bottom shaft unit 104 nestsinto the bottom opening 126 of the spacer 108 and the lower end 120 ofthe top shaft unit 106 nests into the top opening 124 of the spacer 108.The bottom of the spacer 108 abuts against the inner race 112 of theupper bearing 114 in the bottom actuator assembly 118. The top of thespacer 108 may simply abut against the inner race 112 of the upperbearing 114 in the top actuator assembly 122. Alternately, as shown inFIG. 4, an optional flange 128 may be provided near the lower end 120 ofthe top shaft unit 106 and the spacer 108 may abut against that flange128.

FIG. 5 is a side broken view of still a different pivot assembly 10. Asplit shaft assembly 152 is provided which includes a bottom shaft unit154 and a top shaft unit 156. When assembled, the split shaft assembly152 and many of its components share a common pivot axis 158. A top end160 of the bottom shaft unit 154 has a first concentric bushing 162 anda bottom end 164 of the top shaft unit 156 has a second concentricbushing 166 which is axially offset differently than the firstconcentric bushing 162. The bottom shaft unit 154 and the top shaft unit156 are assembled into the split shaft assembly 152 by inter-nestinglyengaging the concentric bushings 162, 166 with a separating layer ofvibration control material 168. Optionally, as shown, the vibrationcontrol material 168 may also fill a gap 170 present between the top end160 of the bottom shaft unit 154 and the bottom end 164 of the top shaftunit 156.

FIG. 6 is a side broken view of another pivot assembly 10. A split shaftassembly 202 is provided which includes a bottom shaft unit 204 and atop shaft unit 206, all having a common pivot axis 208 when assembled.The shaft units 204, 206 each have a respective flange 210 at one endand may, as shown, be the same part but oriented differently whenassembled. One benefit of using exactly the same part in this manner isreducing the variety of parts which must be stocked, and this thepotential cost of disk storage units.

The inner races 212 of bearings 214 in actuator assemblies 216 abutagainst the flanges 210 on one side, and the opposite sides of theflanges 210 are engaged by a layer of vibration control material 218which has adhesive properties in addition to vibration controlproperties. In this manner, the split shaft assembly 202 as a whole hasdesired stiffness in the axial and bending directions and maintains thecommon pivot axis 208.

FIG. 7 is a side broken view of yet another pivot assembly 10. A splitshaft assembly 252 is provided here which includes a hollow bottom shaftunit 254, a hollow top shaft unit 256, and a common inner shaft 258,again all having a common pivot axis 260 when assembled. The shaft units254, 256 are mounted on the common inner shaft 258, but separated fromdirect contact with it by a vibration control material 262.

Conceptually, the embodiment of FIG. 7 may be viewed as a version of theembodiment of FIG. 3 wherein the post 58 is taken to an extreme tobecome the common inner shaft 258. As was the case in FIG. 3, whereoptional bushings 66, 68 where shown, the embodiment in FIG. 7 mayoptionally also employ bushings 264 to yet further provide desiredstiffness in the axial and bending directions and to maintain the commonpivot axis 260.

FIGS. 8a-c (prior art) and FIGS. 9a-c are performance graphs of armresponse for both a standard common shaft pivot assembly the pivotassembly 10 of FIG. 6. Upper and lower range peaks are particularlynoted in each graph.

In FIGS. 8a and 9 a the graphs depict the response at the top arm on abottom actuator when the bottom actuator is the excitation source. Inthe lower range, the prior art system peaks at 3.49 kHz and 136.0 dB,while the inventive pivot assembly 10 peaks at 2.72 kHz and 132.0 dB. Inthe higher range, the prior art system peaks at 7.18 kHz and 139.8 dB,while the inventive pivot assembly 10 peaks at 7.17 kHz and 145.5 dB.Two particular conclusions can be drawn here.

Firstly, there are differences in the peak frequencies and these may bebeneficially employed. This may not be immediately appreciated by thoseused to dealing with prior art systems, since peak frequencies in suchare dependent on the rigid parts used and any degree of control isconsiderably harder to accomplish. However, in the pivot assembly 10 thechoice and application of the vibration control material 218 can easilybe used to specifically control peak frequencies, e.g., to avoidresonant or harmonic frequencies.

Secondly, the peak amplitudes of the respective systems are notablydifferent. In the lower range, the pivot assembly 10 has a clear 4 dBadvantage. In the higher range, however, the peak values taken alone canbe deceptive. While the pivot assembly 10 might appear to suffer a 5.7dB disadvantage, the graph in FIG. 9a is much smoother and the argumentcan be made that the numbers in FIG. 8a are not actually those of thetrue high range peak (if one notes the spike at 9 kHz). Based on theoverall performances depicted, most designers would prefer that depictedin FIG. 9a over that in FIG. 8a.

In FIGS. 8b and 9 b the graphs depict responses at the bottom arm of thetop actuator when the bottom actuator is again the excitation source. Inboth the lower and upper ranges, the inventive pivot assembly 10exhibits striking 13.5 dB advantages, as well as smoother overallresponse curves.

In FIGS. 8c and 9 c the graphs depict responses at the top arm of thetop actuator when the bottom actuator is yet again the excitationsource. In the respective lower and upper ranges, the pivot assembly 10exhibit clear 9.9 and 3.3 dB advantages.

In sum, as FIGS. 8a-c and 9 a-c demonstrate, the inventive pivotassembly 10 has preferable performance criteria over the prior artsystem and its prompt acceptance and use by the industry can beanticipated.

Although this invention has been described with respect to specificembodiments, the details thereof are not to be construed as limitations,for it will be apparent that various embodiments, changes andmodifications may be resorted to without departing from the spirit andscope thereof; and it is understood that such equivalent embodiments areintended to be included within the scope of this invention.

What is claimed is:
 1. A split shaft assembly for vibration controlbetween a first actuator pivot and a second actuator pivot in a diskstorage device, comprising: a first shaft unit, wherein the firstactuator pivot is mounted on said first shaft unit; a second shaft unit,wherein the second actuator pivot is mounted on said second shaft unit;and said second shaft unit is mated to said first shaft unit in axialalignment along a common pivot axis by a separating portion of avibration control material, to interrupt transmission of vibrationalforce between the first actuator pivot and the second actuator pivot. 2.The split shaft assembly of claim 1, wherein: said first shaft unit hasa boss; said second shaft unit has a flange; and said vibration controlmaterial separates said flange from said boss.
 3. The split shaftassembly of claim 2, wherein: said first shaft unit includes a shoulderwhich said boss extends beyond and against which said flange of saidsecond shaft unit abuts, wherein said vibration control material alsoextends between said flange and said shoulder.
 4. The split shaftassembly of claim 1, further comprising: a post having a first end and asecond end; and wherein: said first shaft unit has a first recessreceiving said first end of said post and said vibration controlmaterial separates said first shaft unit from said post; and said secondshaft unit has a second recess receiving said second end of said postand said vibration control material also separates said second shaftunit from said post.
 5. The split shaft assembly of claim 4, wherein:said first shaft unit includes a first bushing proximate to where saidfirst recess receives said post; said second shaft unit includes asecond bushing proximate to where said second recess receives said post;and said vibration control material also separates said first bushingfrom said second bushing, to strengthen said axial aligning of saidsecond shaft unit with said first shaft unit along said common pivotaxis.
 6. The split shaft assembly of claim 4, wherein: at least one ofsaid first shaft unit and said second shaft unit are hollow, therebyforming at least one of said first recess and said second recess.
 7. Thesplit shaft assembly of claim 6, wherein: both said first shaft unit andsaid second shaft unit are hollow, thereby forming both said firstrecess and said second recess; said first end of said post extendsthrough said first recess substantially the entire length of said firstshaft unit and defines a first region between said first shaft unit andsaid post; said second end of said post extends through said secondrecess substantially the entire length of said second shaft unit anddefines a second region between said second shaft unit and said post;said vibration control material is present in substantially all of saidfirst region and said second region, to strengthen said axial alignmentof said second shaft unit with said first shaft unit along said commonpivot axis and to more strongly interrupt said transmission ofvibrational force between the first actuator pivot and the secondactuator pivot.
 8. The split shaft assembly of claim 7, wherein: saidfirst shaft unit includes a first bushing proximate to where said firstrecess receives said post; said second shaft unit includes a secondbushing proximate to where said second recess receives said post; andsaid vibration control material also separates said first bushing fromsaid second bushing, to strengthen said axial aligning of said secondshaft unit with said first shaft unit along said common pivot axis. 9.The split shaft assembly of claim 1, further comprising: a spacer havinga first opening and a second opening which are coaxial, wherein saidspacer is made of said vibration control material; and wherein: saidfirst shaft unit has a first end extending past the first actuatorpivot; said second shaft unit has a second end extending past the secondactuator pivot; and said first end is nested into said first opening ofsaid spacer and said second end is nested into said second opening ofsaid spacer and said first end is separated from contacting said secondend by the presence of said spacer.
 10. The split shaft assembly ofclaim 9, wherein: said spacer has a first side adjacent said firstopening and a second side adjacent said second opening; said first sideof said spacer abuts against the first actuator pivot; and said secondside of said spacer abuts against the second actuator pivot.
 11. Thesplit shaft assembly of claim 10, wherein: at least one of the firstactuator pivot and the second actuator pivot include a bearing racewhich said spacer abuts against.
 12. The split shaft assembly of claim10, wherein: at least one of said first shaft unit and said shaft unitinclude a flange which said spacer abuts against.
 13. The split shaftassembly of claim 1, wherein: said first shaft unit has a first end anda first concentric bushing; said second shaft unit has a second end anda second concentric bushing; said first concentric bushing and saidsecond concentric bushing are axially offset and inter-nestingly engagedalong said common pivot axis, wherein said vibration control materialseparates said first end of said first shaft unit from said secondconcentric bushing and said second concentric bushing from firstconcentric bushing.
 14. The split shaft assembly of claim 13, wherein:said vibration control material also extends between said first end ofsaid first shaft unit and said second end of said second shaft unit. 15.The split shaft assembly of claim 1, wherein: said first shaft unit hasa first end including a first flange; said second shaft unit has asecond end including a second flange; said vibration control materialhas adhesive properties; and said first flange and said second flangeare adhesively engaged by said vibration control material.
 16. The splitshaft assembly of claim 1, wherein: said vibration control material hasat least one member of the set consisting of vibration isolatingcharacteristics and vibration dampening characteristics.
 17. The splitshaft assembly of claim 1, wherein: the disk storage device is amagnetic disk drive; the first actuator is a seeking actuator; and thesecond actuator is a tracking actuator.